Re: [FFmpeg-devel] [PATCH v8 13/18] swscale/ops_backend: add reference backend basend on C templates

From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH v8 13/18] swscale/ops_backend: add reference backend basend on C templates
Date: Sun, 13 Jul 2025 22:14:44 +0200
Message-ID: <GV1P250MB0737833281C64664B29BA2398F55A@GV1P250MB0737.EURP250.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <20250712104459.52153-13-ffmpeg@haasn.xyz>

Niklas Haas:
> From: Niklas Haas <git@haasn.dev>
> 
> This will serve as a reference for the SIMD backends to come. That said,
> with auto-vectorization enabled, the performance of this is not atrocious.
> It easily beats the old C code and sometimes even the old SIMD.
> 
> In theory, we can dramatically speed it up by using GCC vectors instead of
> arrays, but the performance gains from this are too dependent on exact GCC
> versions and flags, so it practice it's not a substitute for a SIMD
> implementation.
> ---
> diff --git a/libswscale/ops.c b/libswscale/ops.c
> index c4f03531eb..2d8f9e6084 100644
> --- a/libswscale/ops.c
> +++ b/libswscale/ops.c
> @@ -27,7 +27,10 @@
>  #include "ops.h"
>  #include "ops_internal.h"
>  
> +extern SwsOpBackend backend_c;

Why are this and the other backends not const?

> +
>  const SwsOpBackend * const ff_sws_op_backends[] = {
> +    &backend_c,
>      NULL
>  };
>  
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